how to find or creat private.pem and public.pem in flutter - flutter

Question

I want use rsa in flutter
I have the following code for flutter
But I do not know about the part test/private.pem and test/public.pem how it is made in flutter
Of course, I have private and public keys that are made in Java with a length of 1024
Can I put them here? Or not, and must the PEM file be created? How do I generate a PEM file?
Thank you for your help
Future<void> main () async {
final publicKey = await parseKeyFromFile<RSAPublicKey>('test/public.pem');
final privKey = await parseKeyFromFile<RSAPrivateKey>('test/private.pem');
final plainText = 'Lorem ipsum dolor sit amet, consectetur adipiscing elit';
final encrypter = Encrypter(RSA(publicKey: publicKey, privateKey: privKey));
final encrypted = encrypter.encrypt(plainText);
final decrypted = encrypter.decrypt(encrypted);
print(decrypted); // Lorem ipsum dolor sit amet, consectetur adipiscing elit
print(encrypted.base64); // kO9EbgbrSwiq0EYz0aBdljHSC/rci2854Qa+nugbhKjidlezNplsEqOxR+pr1RtICZGAtv0YGevJBaRaHS17eHuj7GXo1CM3PR6pjGxrorcwR5Q7/bVEePESsimMbhHWF+AkDIX4v0CwKx9lgaTBgC8/yJKiLmQkyDCj64J3JSE=
}

Answer 1

there are 2 ways to set publicKey and privateKey.
from your project :
create a folder named as test/
inside it
like this
inside private.pem and public.pem paste your private and public key
respectively .
and get it using
final publicKey = await parseKeyFromFile<RSAPublicKey>('test/public.pem');
final privKey = await parseKeyFromFile<RSAPrivateKey>('test/private.pem');
above approach works good when public and private keys are constant
from string :
import 'package:encrypt/encrypt.dart';
import 'package:pointycastle/asymmetric/api.dart';
String privateKeyString="key goes here";
String publicKeyString="key goes here";
//create a instance of RSA key praser
RSAKeyParser keyParser = RSAKeyParser();
//and parse those string keys
RSAAsymmetricKey privateKeyParser = keyParser.parse(privateKeyString);
RSAAsymmetricKey publicKeyParser =keyParser.parse(publicKeyString);
final publicKey = RSAPublicKey(publicKeyParser.modulus!, publicKeyParser.exponent!);
final privKey;
if (privateKeyParser is RSAPrivateKey) {
privKey = RSAPrivateKey(privateKeyParser.modulus!,privateKeyParser.exponent!, privateKeyParser.p,privateKeyParser.q);
final plainText = 'hello world';
final encrypter = Encrypter(RSA(publicKey: publicKey, privateKey:privKey));
final encrypted = encrypter.encrypt(plainText);
final decrypted = encrypter.decrypt(encrypted);
}
it worked for me!!

Answer 2

You can use pointy castle package to do that: https://pub.dev/packages/pointycastle
Just generate a key pair (code below) and use it in your app. Good luck!
import 'package:pointycastle/export.dart';
import 'dart:math';
import 'dart:typed_data';
AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey> generateRSAkeyPair(
SecureRandom secureRandom,
{int bitLength = 2048}) {
// Create an RSA key generator and initialize it
final keyGen = RSAKeyGenerator()
..init(ParametersWithRandom(
RSAKeyGeneratorParameters(BigInt.parse('65537'), bitLength, 64),
secureRandom));
// Use the generator
final pair = keyGen.generateKeyPair();
// Cast the generated key pair into the RSA key types
final myPublic = pair.publicKey as RSAPublicKey;
final myPrivate = pair.privateKey as RSAPrivateKey;
return AsymmetricKeyPair<RSAPublicKey, RSAPrivateKey>(myPublic, myPrivate);
}
SecureRandom exampleSecureRandom() {
final secureRandom = FortunaRandom();
final seedSource = Random.secure();
final seeds = <int>[];
for (int i = 0; i < 32; i++) {
seeds.add(seedSource.nextInt(255));
}
secureRandom.seed(KeyParameter(Uint8List.fromList(seeds)));
return secureRandom;
}
// here is how you generate key pair
final pair = generateRSAkeyPair(exampleSecureRandom());
final public = pair.publicKey; // to get public
final private = pair.privateKey; // i know, you get it :D